1. Define lex and yacc tools
Lex:- scanner that can identify those tokens
Yacc:- parser.yacc takes a concise description of a grammar and produces a C routine that can parse that grammar.
2. Give the structure of the lex program
3. The lexer produced by lex in a ‘c’ routine is called yylex()
4. Explain yytext?
contains the text that matched the pattern.
5. The yacc produced by parser is called yyparse().
6. Why we have to include ‘y.tab.h’ in lex?
y.tab.h contains token definitions eg:- #define letter 258.
7. Explain the structure of a yacc program?
8. Explain yyleng?
Yyleng-contains the length of the string our lexer recognizes.
9. Features of unix
multitasking,mutiuser,online help facility,security,file & process.
10. What is an internal command?give an example?
Command which is shell built-in eg:echo
11. What is an external command?give a example?
Command which resides in other directories-eg:cd in /bin
12. What is an absolute path name?give an example?
A file name identification with respect to the root. Eg:- /home/kumar/f1
13. Differentiate the commands cp and mv?
Cp- copy the files
mv- renaming the file.
14. Explain mkdir command?
Used to create a directory
15. What are tokens or terminal symbols?
Symbols that appear in the input are returned by the lexer are terminal symbols.
16. What type of data structures is used by shift/reduce parsing?
17. Shell- it is a command interpreter
kernel- is the core of the operating system.
18. What is lexical analyzer?
Lex taking a set of descriptions of possible tokensand producing a ‘C” routine is called a lexical analyzer (or) lexer (or) scanner.
19. Define grammer?
The list of rules that define the relationship that the program understands is a grammar.
20. What is symbol table?
The table of words is a simple symbol table,a common structure in lex and yacc applications.
21. What is pseudo token
A pseudo token standing for unary minus, has no associativity is at the highest precedence.
22. What does $$ represents?
$$ represents the value of the left hand side.
23. What are shell scripts?
Using a program, we can run more than one command.
24. What is the usage of grep command?
Grep command is used to search a pattern in a database.
25. What is exit status command?
Exit 0- return success,command executed successfully.
Exit 1 – return failure.
26. What are daemons?
They are one system processes
tells you the name of the unix system you are using.
tells unix which permissions to give to files and directories you create.
displays the device name of your terminal
30. Vi editor
(visual editor)- used to write programs.
lists the attributes of a file.
32. What is an relative path name?
A file identification not with respect to the root.